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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id g185sm43692wmf.30.2019.05.07.13.12.29 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 07 May 2019 13:12:30 -0700 (PDT) Date: Tue, 7 May 2019 22:12:28 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Borislav Petkov , Rik van Riel , Sebastian Andrzej Siewior , x86-ml , lkml Subject: Re: [GIT PULL] x86 FPU changes for 5.2 Message-ID: <20190507201228.GA64489@gmail.com> References: <20190507132632.GB26655@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Linus Torvalds wrote: > On Tue, May 7, 2019 at 6:26 AM Borislav Petkov wrote: > > > > This branch contains work started by Rik van Riel and brought to > > fruition by Sebastian Andrzej Siewior with the main goal to optimize > > when to load FPU registers: only when returning to userspace and not > > on every context switch (while the task remains in the kernel). > > I love this and we should have done it long ago, but I also worry that > every time we've messed with the FP state, we've had interesting bugs. > Which is obviously why we didn't do this long ago. > > Has this gone through lots of testing, particularly with things like FP > signal handling and old machines that don't necessarily have anything > but the most basic FP state (ie Pentium class etc)? > > I've pulled it, but I'd still like to feel safer about it > after-the-fact ;) Most of the x86/fpu commits except the final one are several weeks old, but I have to admit that our old-systems testing is hit and miss, and FPU bugs do tend to have an additional 'bug report latency' multipier of a factor of 3 or so ... I've been running all this (modulo the final commit) on my primary desktop and other systems as well, FWIIW. Thanks, Ingo